1. Field of the Invention
The present invention relates to a fluorescent lamp device, and more particularly, to a flat-type fluorescent lamp device and a method of fabricating a flat-type fluorescent lamp device.
2. Background of the Related Art
Currently, cathode ray tubes (CRTs) are commonly used in televisions, as monitors in scientific instruments, and information terminals. However, the CRTs have size and weight limitations that are in direct opposition to the trend of electronic products becoming smaller and lighter. Different types of flat display devices that are expected to replace the CRTs include liquid crystal display (LCD) devices that make use of electro-optical effects, plasma display panel (PDP) device that make use of gas-discharge, and electro-luminescent display (ELD) device that make use of electroluminescent materials.
Among these flat display devices, the LCD devices have been commonly selected to replace the CRTs because of their small size, light weight, and low power consumption. Since most of the LCD devices are light receptive devices, wherein a quantity of light receivable from an exterior source is controlled to display image data, i.e., pictures, a separate light source for illuminating an LCD panel is necessary. Generally, a backlight unit is used as the light source of the LCD device and includes cylindrical fluorescent lamps. The backlight unit may be divided into different functional categories including bottom-type and edge-type backlight units.
The bottom-type backlight unit includes a plurality of lamps arranged along a first direction beneath a spreading plate for directing light toward a front surface of the LCD panel. The bottom-type backlight unit has a high light utilization efficiency as compared to the edge-type backlight unit, and is commonly used in large sized LCD panels requiring high luminance. However, incorporation of the bottom-type backlight in a thin LCD panel is limited because a gap is required between the lamps and the LCD panel in order to prevent the lamps from being visible on the LCD panel.
The edge-type backlight unit includes a fluorescent lamp at a side of a light plate for spreading the light to an entire surface of the LCD panel through the light plate. The edge-type backlight unit is commonly used in comparatively small sized LCD devices, such as monitors for laptop and desktop computers. However, incorporation of the edge-type backlight unit results in low luminance since the fluorescent lamp is provided at the side of the light plate. Accordingly, the edge-type backlight unit requires high optical design and processing technologies of the light plate for obtaining a uniform distribution of light intensity across an entire surface of the LCD panel.
FIG. 1 is a cross sectional view of an edge-type backlight unit according to the related art. In FIG. 1, a backlight unit is mounted on an under side of an LCD panel that displays image data and includes a lower cover 3 for protecting a base 1, a lamp assembly 10 for holding a lamp to be used as a light source, a light plate 5 for uniform supply of a light from the source to the LCD panel, an upper spreading plate 9 and a lower spreading plate 6 over the light plate 5 for spreading the light from the light plate 5, and an upper prism 8 and a lower prism 7 between the upper spreading plate 9 and the lower spreading plate 6 for converging and directing the light toward the LCD panel.
FIG. 2 is a perspective view of an edge-type backlight unit according to the related art. In FIG. 2, an edge-type backlight unit includes a lamp having a high voltage side lamp wire 13a and a low voltage side lamp wire 13b connected to a connector 16 in a high voltage side lamp holder 12a and a low voltage side lamp holder 12b, respectively. In addition, the lamp wires 13a and 13b are soldered to a high voltage side and a lower voltage side of the lamp, respectively, and lamp holders 12a and 12b are attached to cover the soldered part of the lamp. The lamp is placed in a lamp housing 15.
Next, the lamp assembly is mounted onto a base 1, and a lower cover 3 is attached to a part of the base 1 around a light reception part of a light plate 5. This protects the lamp assembly from external impact. After a reflective plate 4 is placed on an inside bottom of the base 1, the light plate 5 is inserted in an inside of an inner cap part of the lamp housing 15 without deforming the inside cap of the lamp housing 15. A lower spreading plate 6, a lower prism 7, an upper prism 8, and an upper spreading plate 9 are sequentially placed on the light plate 5.
When power is provided to the backlight unit through the connector 16 connected to a power source, light is emitted from the lamp as a glow discharge. Accordingly, the emitted light is incident on a light reception surface of the light plate 5, and is reflected and scattered by dots printed on a bottom of the light plate 5. The light is scattered along an oblique direction as it passes through the spreading plate 6, which is arranged along a vertical direction as the light passes through the upper and lower prisms 8 and 7. The light is scattered again along an oblique angle as the it passes through the spreading plate 9. Eventually, a portion of the light passed through the spreading plate 6 illuminates the LCD panel from a back surface. Thus, when the reflective plate 4 reflects the light, the light escapes to a back surface without being reflected and scattered by the printed dots on the light plate 5, and is transmitted upward again.
However, the backlight unit has the following disadvantages. First, since the light progresses along a lateral direction from the fluorescent lamp, the backlight unit cannot provide adequate amounts of light. Accordingly, uniform luminance cannot be provided along an entire surface of the LCD panel. Second, it is very difficult to control a surface state of the light plate and a direction of the light progression by using the light plate having the fixed pattern of printed dots. Third, the fabrication process is complicated, thereby resulting in poor device yield. For example, many defects may be generated during the fabrication process, including deformed light plates or light plates having inaccurate dimensions. Specifically, since there are different thermal expansion coefficients between the different sheets and structures, wrinkles are generated. In addition, large dimensional variations of the light plate are caused by high absorption of moisture when the LCD panel and backlight unit are exposed to high humidity. Fourth, measures to prevent contamination by foreign matter and to prevent scratches on the light plate and sheets increase production costs.
FIG. 3 is a cross sectional view of a flat-type fluorescent lamp device according to the related art, and FIG. 4 is a cross sectional view and a plan view of dark spots on the flat-type fluorescent lamp device in FIG. 3 according to the related art. In FIGS. 3 and 4, a flat-type fluorescent lamp device includes a plurality of first and second electrodes 31 and 32 arranged on a first substrate 30 at fixed intervals, a barrier layer 33 covering an entire surface of each of the first and second electrodes 31 and 32, a first fluorescent layer 34 on an entire surface of the first substrate 30 including the first and second electrodes 31 and 32 and the barrier layer 33, a second fluorescent layer 41 on a second substrate 40, and supports 42 formed between the first substrate 30 and the second substrate 40.
The first and second substrates 30 and 40 may be formed of glass or heat resistive flat material. The barrier layer 33 is formed of a material that can function as a reflective layer for directing UV light along an upward direction. The support 42 is arranged between the first and second substrates 30 and 40, and supports the first and second substrates 30 and 40, wherein sides of the support 42 are concave for providing improved discharge efficiency. In addition, side supports 43 provide support for the first substrate 30 and the second substrate 40, and confine an inert gas, such as Xe, between the first and second substrates 30 and 40.
In FIG. 3, upon application of a voltage to the first and second electrodes 31 and 32, electrons emitted from the first electrode 31 collide with atoms of the inert gas to form a plasma that emits UV light. Then, the UV light collides with the second fluorescent layer 41 on the second substrate 40 to cause the second fluorescent layer 41 to emit white light. Accordingly, the white light passes through the second substrate 40 to emit a light from an entire upper surface of the second substrate 40. However, the UV light cannot transmit through the supports 42, and this dark spots are formed in areas of the fluorescent layer 41 where no white light is transmitted. Accordingly, since the dark spots deteriorate a uniform intensity of the white light, an additional spreading film must be incorporated. The spreading film decreases productivity, increases weight, and decreases an overall luminance of the flat-type fluorescent lamp device. Moreover, the process required for attaching the supports 42 between the first and the second substrates 30 and 40 at required positions further decreases productivity.